The present invention concerns a bearing arrangement for a shaft supporting a rotating tool, with the shaft being axially unshiftable in a fixed roller bearing on one side of the tool and rotatable at its free end on the other side of the tool at least indirectly in a roller bearing which is axially removable for replacement of the tool, the latter bearing being axially secured with its outer ring in a shiftable bearing block and secured inwardly possibly via an inner ring on a bearing sleeve slidable onto the free shaft end.
Such a bearing arrangement finds use especially in rolling mills in which the profiling rolls serving as tools need to be replaced relatively often, for which purpose one of the roller bearings needs to be removed in order to be able to remove the profiling roll from the shaft and replace it with another profiling roll. However, further applications are also conceivable for such a bearing arrangement, for example, in portal milling machines in which a bearing of the milling shaft likewise needs to be removed for tool replacement. In describing the present invention in the following, for purposes of simplicity, reference is made only to its use in rolling mills without any intention, however, of limiting the range of application of the present invention.
In modern heavy-duty rolling mills such as are used, for example, in manufacturing thick-walled precision tubes, a high rotational accuracy of the replaceable profiling rolls is required, which should be better than 0.01 mm, if possible. In addition, high rolling forces need to be produced, which assumes a corresponding rigidity of the roll-supporting frame. Since the rolls often need to be changed several times in a day, such replacement must be possible in a short time in order to keep production costs as low as possible. Finally, long operating periods and short periods for maintenance and servicing are required.
It follows from this list of requirements that the rolls need to be positioned between two roll stands having roller bearings for the roll shaft. Rolls positioned on overhung shafts, commonly employed for easy and rapid replaceability, can not be used since such rolls do not permit the occurrence of high rolling forces.
With respect to the required long operating periods and freedom from maintenance, all of the structural elements used in the bearing arrangement additionally need to be durable. In particular, no fretting corrosion may occur at the points of contact between highly stressed parts.
Designs known up to now could not supply any technically satisfactory solution for the arrangement of the removable roller bearing since, in these designs, the roller bearing is slid via a bearing sleeve with cylindrical borehole onto a cylindrical outer surface of the free end of the shaft, with the result that fretting corrosion forms after a short period at this interface, which exhibits slight play for assembly reasons, due to the micromovements caused by the rolls.
The object of the present invention is therefore to develop, for a bearing arrangement of the above-mentioned type, a shiftable bearing for tool replacement such that the associated structural elements are arranged mutually play-free and additionally make possible a reduction of the bearing play fundamentally inherent in the associated roller bearing. Here, the new design should range within the framework of the previous cost of structural parts and should be relatively simple and economical.
Based on a bearing arrangement of the type mentioned above, this problem is solved according to the present invention in that the seating of the bearing sleeve borne at least indirectly by the shaft is formed by a conical outer surface that tapers toward the shaft end, that the bearing sleeve includes a conical borehole corresponding to the conical outer surface, and that the bearing sleeve is radially expanded via a stop-limited axial shifting with respect to the conical outer surface by an amount giving a specific level of reduced roller-bearing play.
These inventive measures have the effect that the press fit of the bearing sleeve on the free shaft end, a fit which can be loosened for removal of the roller bearing, is now pretensioned in the assembled state and therefore designed to be completely free of play. Therefore, the conditions for forming fretting corrosion there are eliminated. In addition, as a result of the conical seating of the bearing sleeve on the free shaft end, the bearing sleeve can be expanded by a specific amount through corresponding shifting with respect to the free shaft end so that the bearing play fundamentally inherent in the roller bearing can be reduced, if necessary, to a minimum through simultaneous corresponding expansion of the roller-bearing inner ring. Here, the degree of this expansion is limited or defined by the mentioned stop for the shifting of the bearing sleeve so that, after removal of the roller bearing for changing of the profiling rolls, reinstallation of the roller bearing again produces the same seating conditions.
In this way, a bearing arrangement for the profiling rolls of rolling mills is provided which can accommodate large roll forces with maximum rotational accuracy without the danger that manifestations of wear can be produced within the removable bearing system through the formation of fretting corrosion. On the other hand, the design of the present invention ranges as regards its construction costs and space requirements within the previous framework and thus avoids additional expenditures for maintenance and servicing. At the same time, an increase in service life is possible through elimination of wear possibilities.
The conical outer surface can be formed directly by the free end of the shaft. However, depending on the details of machine design, especially with regard to the mounting of the profiling rolls, the conical outer surface can also be formed by a metal conical sleeve tightly joined to the free shaft end. The sleeve permits the assembly of structural parts for securing the profiling rolls prior to its positioning on the free shaft end. In order that freedom from play between the conical sleeve and the shaft end is now also guaranteed, it is appropriate to shrink-fit the conical sleeve on the free shaft end. Instead of this or also additionally, it can be provided that the conical sleeve abuts on the end wall of the free shaft end via a radially inwardly directed circular flange, and that flange and shaft end are detachably joined together via screw means.
With respect to the taper of the mating conical outer surface at the shaft end and the conical borehole of the bearing sleeve with respect to their axis, this appropriately exhibits an angle above the effective angle of friction so that no additional resistance opposes the loosening of the removable bearing. Assuming that the mating of the conical outer surface and the conical borehole is appropriately lubricated with molybdenum disulfide, a conical angle of about 7xc2x0 with respect to the shaft axis can be utilized.
With respect to the more detailed construction of the seating of the bearing sleeve on the free shaft end, it has proven advantageous for the bearing sleeve to include a radially inwardly directed collar as a stop, and for the collar with its radial surface facing the shaft to be held in contact with the radial end wall of the free shaft end or the free end wall of the conical sleeve. It is advantageous for this mounting arrangement that a protruding fastening bolt be secured in a concentric borehole of the free shaft end, that a disk-shaped tightening plate in contact with the collar be located in a terminal, axis-parallel, collar-bordering borehole of the bearing sleeve, that the fastening bolt penetrate a central borehole of the tightening plate with its end exhibiting external threading, and that the collar of the bearing sleeve be tightened against the end wall of the shaft end or the conical sleeve by a nut screwed on the external threading against the tightening plate. Here, in order to facilitate assembly, the tightening plate can be removably joined with the bearing sleeve via screw means connecting it with the collar.
As already described, by placing the collar of the bearing sleeve against the end wall of the free shaft end, the radial expansion of the bearing sleeve and, if necessary, the inner ring of the roller bearing is basically predetermined, and thus the restriction of roller bearing play in its order of magnitude. However, in order to ensure maximum precision here and compensate for any production tolerances or eliminate their effects, it has proven to be advantageous in final machining of the roller-bearing-supporting cylindrical outer surface of the bearing sleeve for the sleeve collar to be tightenable against the involved end wall via screw means penetrating the collar and passing into the end wall of the shaft end or the conical sleeve. Here, the bearing sleeve is thus temporarily mounted in secure fashion on the shaft end or on the conical sleeve borne by the shaft end without the subsequently employed means in the form of tightening plate and fastening bolt in a manner which withstands the forces occurring during the machining of the outer surface of the bearing sleeve. Now the shaft can be supported between tips in a suitable tooling machine and the final finishing of the outer surface of the bearing sleeve can be undertaken to such an extent as corresponds to the desired reduction of play in the roller bearing subsequently borne by the outer surface.
In order that the result of this highly precise finishing is also retained during later use, it is appropriate that the mutual position of bearing sleeve and shaft or conical sleeve be fixed in the peripheral direction. This positioning can be provided by an index pin extending parallel to the axis of the shaft and into a borehole in the collar and the end wall or the conical sleeve.
In order to keep impurities from getting into the conical mating between the shaft end or conical sleeve and the bearing sleeve during operation, it is advantageous for the bearing sleeve to include a circular seal in contact with the neighboring inner part in the area of its end surrounding the shaft.
Finally, the bearing sleeve can be designed as a structural unit closed in the peripheral direction. The radial expansion of the bearing sleeve resulting during tightening is only in the range of a few 1/100 mm at a distance of about 0.6 mm between the collar of the bearing sleeve and the end wall of the shaft or the conical sleeve prior to tightening. Depending on the circumstances of the individual case, there exists, however, the possibility for providing the bearing sleeve with longitudinal slots for easier expansion. However, in this case, the longitudinal slots should appropriately be filled in with elastic sealing material in order to prevent penetration of dirt into the area of the conical mating of bearing sleeve and shaft or conical sleeve.